An RFID radio interface specification (i.e., ISO/IEC 18000-6) is developed to include an RFID architecture (i.e., RFID portals), to remarkably reduce a communication error generated due to an inter-tag interference, etc. while easily detecting and controlling the communication error.
However, recently, as a handheld-based RFID interrogator occupies a great part, a necessity for a technique to secure effective use of an RFID technology in a mobile application is on the rise. In particular, compared with most of static scenarios, a position and local arrangement of an active mobile device, for example, a distance from a target and a direction of an antenna cannot be fundamentally predicted. That is, it is actually difficult to determine the number of RFID interrogators that are asynchronously operated compared with tag detection in the same frequency channel.
Currently, RFID interrogators close to each other are connected to each other by wires to be synchronized, but such hard-wired synchronization cannot be adopted in the mobile application. Of course, theoretically, the synchronization may be adopted in a radio communication environment. However, up to now, since the position of the RFID interrogator cannot be found, an additional channel is required to synchronize an RFID handheld device.
Listen before talk (LBT) which is mandatorily used in Europe is used as another mechanism for preventing a plurality of RFID interrogators from being activated at the same time. However, the LBT is not effective in a mobile RFID. The reason for this is that since the arrangement of the RFID interrogator considerably varies, a threshold of available reception sensitivity cannot be determined.
In addition, a method for overcoming unintentional collision of the adjacent RFID interrogators includes time division multiplexing (TDM), frequency division multiplexing (FDM), etc. However, when temporal synchronization is not supported or only one channel is assigned to the mobile RFID, the mechanisms cannot be adopted in the mobile RFID. In other words, the RFID interrogator cannot be discriminated from tag communication with clarity and in the spectrum.
In order to effectively use the RFID interrogator in the mobile environment, the RFID interrogator must adapt to the communication error, which is currently on the rise in the mobile environment. However, currently, a general RFID radio interface specification such as ISO/IEC 18000-6 Type C has no restriction with respect to the number of command timings that the interrogator can retransmit or a condition for retransmitting the commands in the case in which a failure occurs during an inventory round. Further, a method for finding a reasonable compromise point between collision avoidance and processing performance is required with respect to a reference range for selecting a random wait time for retransmitting the commands.
Another objects and advantages of the present invention can be appreciated by the following description and will be clearly described by the embodiments of the present invention. Further, it will be easily known that the objects and advantages of the present invention can be implemented by means and a combination thereof shown in the appended claims.